Glycosaminoglycans (GAGs) are linear, acidic polysaccharides that exist ubiquitously in nature as residents of the extracellular matrix (ECM) and at the cell surface, as constituents of proteoglycans, of many different organisms of divergent phylogeny (Habuchi, O. (2000) Biochim Biophys Acta 1474, 115-27; Sasisekharan, R., Bulmer, M., Moremen, K. W., Cooney, C. L., and Langer, R. (1993) Proc Natl Acad Sci. USA 90, 3660-4). Glycosaminoglycans consist of a disaccharide repeat unit of a hexosamine linked to an uronic acid. These sugars, apart from having important structural roles in the ECM, are also fundamental modulators of many biological processes like development, cell proliferation, signaling and inflammation (Bernfield, M., Gotte, M., Park, P. W., Reizes, O., Fitzgerald, M. L., Lincecum, J. and Zako, M. (1999) Functions of cell surface heparan sulfate proteoglycans. Annu Rev Biochem 68, 729-777; Sugahara, K., Mikami, T., Uyama, T., Mizuguchi, S., Nomura, K. and Kitagawa, H. (2003) Recent advances in the structural biology of chondroitin sulfate and dermatan sulfate. Curr Opin Struct Biol 13, 612-620.) GAGs act as critical modulators of a number of biochemical signaling events (Tumova, S., Woods, A., and Couchman, J. R. (2000) Int J Biochem Cell Biol 32, 269-88) requisite for cell growth and differentiation, cell adhesion and migration, and tissue morphogenesis. Chondroitin sulfate (CS)/dermatan sulfate (DS) polysaccharides have been implicated in a variety of biological phenomena ranging from anticoagulation to osteoarthritis (Mascellani, G., Liverani, L., Bianchini, P., Parma, B., Torri, G., Bisio, A., Guerrini, M., and Casu, B. (1993) Biochem. J. 296, 639-48; Achur, R. N., Valiyaveettil, M., Alkhalil, A., Ockenhouse, C. F., and Gowda, D. C. (2000) J. Biol. Chem. 275, 40344-56; and Plaas, A. H., West, L. A., Wong-Palms, S., and Nelson, F. R. (1998) J. Biol. Chem. 273, 12642-9). In addition, modification of existing GAG sequences by chondroitinase ABC and chondroitinase AC may inhibit angiogenesis and tumor metastasis (Denholm, E. M. et al. (2001) Eur. J. Pharmacol. 416, 213-21).
The chemical heterogeneity of GAGs is responsible for their wide-ranging biological influence. Each GAG disaccharide repeat unit can be customized through a variety of biosynthetic modifications that include epimerization of the uronic acid and variable sulfation. The specific sequence of chemical modifications on GAG chains imparts a potential for interaction with other biological agents, including growth factors, cytokines, and other signal transducers. Even more, specific sequences within the oligosaccharide chain have been shown to be activating, and others inhibitory, with regard to specific biological processes (Bao, X., Nishimura, S., Mikami, T., Yamada, S., Itoh, N. and Sugahara, K. (2004) Chondroitin sulfate/dermatan sulfate hybrid chains from embryonic pig brain, which contain a higher proportion of L-iduronic acid than those from adult pig brain, exhibit neuritogenic and growth factor binding activities. J Biol Chem 279, 9765-9776.) This emerging paradigm of structure-function glycobiology promises to create new strategies for the crafting of medical interventions.
The development of complementary biochemical tools that cleave GAGs in a sequence-specific fashion has enabled progress in the polysaccharide sequencing field. Many microorganisms express GAG-degrading enzymes for the purpose of facile invasion of host tissue and to acquire nutrition from decaying animal tissues (Ernst, S., Langer, R., Cooney, C. L. and Sasisekharan, R. (1995) Enzymatic degradation of glycosaminoglycans. Crit Rev Biochem Mol Biol 30, 387-444.) A number of these enzymes have been cloned and sequenced and are being developed in polysaccharide sequencing methodologies and other industrial applications. These include heparinases I, II, and III and chondroitinases AC and B (cAC and cB, respectively) from Flavobacterium heparinum (Venkataraman, G., Shriver, Z., Raman, R. and Sasisekharan, R. (1999) Sequencing complex polysaccharides. Science 286, 537-54; Sasisekharan, R., Bulmer, M., Moremen, K. W., Cooney, C. L. and Langer, R. (1993) Cloning and expression of heparinase I gene from Flavobacterium heparinum. Proc Natl Acad Sci U S A 90, 3660-3664; Godavarti, R., Davis, M., Venkataraman, G., Cooney, C., Langer, R. and Sasisekharan, R. (1996) Heparinase III from Flavobacterium heparinum: cloning and recombinant expression in Escherichia coli. Biochem Biophys Res Commun 225, 751-758; Pojasek, K., Shriver, Z., Kiley, P., Venkataraman, G. and Sasisekharan, R. (2001) Recombinant expression, purification, and kinetic characterization of chondroitinase AC and chondroitinase B from Flavobacterium heparinum. Biochem Biophys Res Commun 286, 343-351.) Overall, the role of GAGs as specific mediators of tumorigenesis and other biological events is an emerging field that offers the potential for the development of novel therapeutics (Shriver, Z. et al. (2002) Trends. Cardiovasc. Med. 12, 71-7; and Liu, D. et al. (2002) Proc. Natl. Acad Sci. USA 99, 568-73).